1. Field of the Invention
The present invention relates to a stopper for a cylindrical elastic mount and a cylindrical elastic mount assembly, in particular to a stopper for cylindrical elastic mount that is suitably used as a discrete stopper assembled to a cylindrical elastic mount such as a differential mount, a member mount or a body mount for an automobile, as well as a cylindrical elastic mount constructed by assembling such stopper.
2. Discussion of Related Art
As a type of an elastic mount interposed between two members to connect these two members, a first member and a second member constituting a vibration transmission system, there is known a cylindrical elastic mount which includes a predetermined shaft member, an outer cylindrical member disposed radially outwardly of the shaft member with a distance therebetween and a main elastic rubber body interposed therebetween for elastic connection. In the cylindrical elastic mount structured as above, generally, the shaft member is fixed to the first member by a fixing bolt inserted into an inner hole of the shaft member, and the outer cylindrical member is fixed to the second member by press-fitting in an attachment hole formed therein. When a vibration load (vibration) is applied in an axial direction or perpendicular to an axial direction between the shaft member and the outer cylindrical member, the main elastic rubber body is elastically deformed to absorb the vibration. Thus, the cylindrical elastic mount is suitably used as a differential mount, a member mount, a body mount or the like for a vehicle such as an automobile.
Meanwhile, many of cylindrical elastic mounts structured as above include a stopper means for limiting an amount of an axial relative displacement between the shaft member and the outer cylindrical member to prevent an excessive deformation of the main elastic rubber body when a large vibration load is axially applied. Such stopper means is provided to achieve an improvement in durability of the main elastic rubber body or other purposes. In addition, as a kind of the conventional stopper means, a stopper for a cylindrical elastic mount has been suitably used as shown in FIG. 4 of JP-A-2004-28250. The stopper for a cylindrical elastic mount is a discrete stopper, which is a distinct member from the cylindrical elastic mount and is assembled to a first axial end of the cylindrical elastic mount.
The discrete stopper includes a stopper fitting fixed to a first axial end of a shaft member by a fixing bolt in a state of being opposed to a second member and an outer cylindrical member, and a rubber portion fixedly disposed on a surface where the stopper fitting is opposed to those members. When the shaft member and the outer cylindrical member are subjected to excessive relative displacement toward their first axial ends, the second member or the outer cylindrical member are brought into abutting contact with the stopper fitting via the rubber portion, whereby the axial relative displacement toward the first axial ends of the shaft member and the outer cylindrical member can be elastically limited. An axial relative displacement toward second axial ends of the shaft member and the outer cylindrical member is generally limited by abutting an outer flange, which is disposed along a periphery of an end of the outer cylindrical member located on a second axial end side of the cylindrical elastic mount, against the first member via a rubber stopper formed integrally with the main elastic rubber body.
Additionally, as shown in FIGS. 3 and 6 of JP-A-2004-28250, there is also known a discrete stopper having two rubber portions disposed on a stopper fitting, in which a first rubber portion has a height lower than a second rubber portion, and the second rubber portion has a tip located closer to the second member and the outer cylindrical member than a tip of the first rubber portion.
The known discrete stopper, in a state of being assembled to a cylindrical elastic mount, is capable of exhibiting a stopper function for limiting the amount of relative displacement toward the first axial end side of the shaft member and the outer cylindrical member via the first rubber portion having the lower height. Then, the second rubber portion, which is in a state of being in contact with the second member and the outer cylindrical member, is subjected to elastic compressive deformation so as to allow the axial relative displacement between the shaft member and the outer cylindrical member until the members abut on the first rubber portion. Thereby, in cooperation with shearing deformation of the main elastic rubber body, there is exhibited a vibration damping function to absorb a vibration load applied axially between the shaft member and the outer cylindrical member.
Particularly in the discrete stopper shown in FIG. 6 of JP-A-2004-28250, the stopper fitting has a cylindrical shape having a bottom portion on one side thereof and opening toward the second member side. Additionally, the stopper fitting includes an outward flange that is integrally formed along a periphery of an opening-side end of the cylindrical portion. In the above discrete stopper, the first rubber portion is fixedly disposed on the outward flange of the stopper fitting, and the second rubber portion is fixedly disposed on the bottom portion thereof. The cylindrical portion connecting the outward flange and the bottom portion is disposed radially outwardly of the shaft member of the cylindrical elastic mount with a radial distance therebetween. The bottom portion is supported by the shaft member at its center. With the first and the second rubber portions are opposite to or in contact with the second member, the discrete stopper is assembled to the first axial end of the cylindrical elastic mount.
Consequently, the discrete stopper structured as above is different from the known discrete stopper in which the first and the second rubber portions are fixedly disposed on a one-side surface of the stopper fitting made of a flat plate, as shown in FIG. 3 of JP-A-2004-28250. The discrete stopper shown in FIG. 6 of the patent publication document allows an increase in the height of the second rubber portion without changing a distance between the second member or the outer cylindrical member and the first rubber portion. This can reduce a spring constant of the second rubber portion subjected to a compressive deformation, that is, the vibration damping performance can be improved without changing a limit position of the axial relative displacement toward the first axial end sides of the shaft member and the outer cylindrical member limited by contacting those members with the first rubber portion.
The inventors of the present invention have made an extensive study on the discrete stopper constructed as described above, and have found that the known discrete stopper has internal problems as below.
Specifically, in the known discrete stopper having the first and the second rubber portions, for ensuring a sufficient durability of the first rubber portion, it is desirable to provide a largest possible area for contacting the first rubber portion with the second member and the outer cylindrical member. In addition, it is preferable that the second rubber portion also has sufficient height and thickness for reducing a spring constant so as to improve vibration damping performance thereof without sacrificing durability.
However, in the known discrete stopper, the first and the second rubber portions are disposed on the outward flange and the bottom portion such that they are located on an outer and inner side of the stopper fitting in the radial direction, respectively. In this case, the stopper fitting is supported at its center by the shaft member of the cylindrical elastic mount. Accordingly, in the stopper fitting, a limited narrow area is provided as a space for forming the outward flange and the bottom portion where the first and the second rubber portions are fixedly disposed. Thus, in the limited narrow area of such a stopper fitting, it has been difficult to dispose together both of the first rubber portion having the largest possible area for contacting with the second member, and the outer cylindrical member and the second rubber portion having the sufficiently large height and thickness. Therefore, in the known discrete stopper, namely, in the above stopper for a cylindrical elastic mount, it has been extremely difficult to simultaneously ensure sufficient durability and high vibration damping performance or vibration damping characteristics.